The global universality of the Internet Protocol (IP) has provided the incentive to make available to end users an ever increasing range of communication related services. These services include interactive communications such as voice, video and interactive games. Of particular significance is the Session Initiation Protocol (SIP) which has enabled the delivery of a wide range of enhanced telephony services. Through such telephony services end users can obtain the convergence of data and voice using packet telephony. These include an IP telephony (IPT) and multimedia application which provides IP based telephony services (voice, video and data) between two native IP terminals, or between an IP terminal and a normal POTs subscriber through an accessible IP gateway. The IPT applications can support black phones behind access gateways, residential gateways or integrated access devices. The IPT services both the residential and business markets and offers a wide range of managed VOIP-VPN services typically targeted at enterprise interconnection.
The long distance bypass (LDB), another telephony service, enables service providers to use packet based networks for basic long distance voice traffic thereby bypassing the traditional trunk, toll and international exchanges and optimizing voice transit costs.
Typically, such services are provided using a signalling proxy server, examples of such being Alcatel 5450 and Alcatel 5020.
Although VoIP promises significant cost savings and user convenience, without the introduction of proper controls it will be subject to abuse. It is well known that users of e-mail services over IP are constantly being bombarded with unsolicited correspondence known generally as Spam. Likewise, users of the ubiquitous PSTN are bothered with unsolicited telephone calls from Telemarketers, advertisers and the like. If left unchecked, unsolicited sessions such as telephone calls via VoIP will harm or even render impractical the service as businesses and consumers alike will react unfavorably to the service challenge.
E-mail and instant messaging (IM) are both subject, of course, to Spam but it can be controlled to some extent through filters which block or intercept certain messages. These filters provide a measure of protection as they are able to analyze text for its content before accepting or rejecting the correspondence. Such is not the case for voice messages, however, when it is impossible to predetermine the content of a future voice session.
Traditional voice networks employ services such as privacy detectors to deal with potentially annoying calls. An example of such a detector is a BellSouth Privacy Detector which can decrease the number of disruptive calls thereby giving consumers an increased sense of control, privacy and security within their own home. The Privacy Detector intercepts calls for which the caller's number is one of: blocked; private; unknown; or unavailable and requires those callers to identify themselves before their call can ring through on the customer's telephone. Another known system employs a “do not call” list that is used to identify recipients that do not wish to receive unsolicited calls from commercial organizations.
In connection with interactive communication sessions including VoIP, an entity attempting to make an unsolicited call known herein as a spammer, can adopt Spam techniques developed to automatically generate unsolicited VoIP phone calls, video session, chat sessions for commercial or even elicit purposes. The difficulty in detecting and controlling the impact of VoIP Spam is compounded by the fact that VoIP Spam initiators may be different from the source of the Spam content such as pre-recorded messages, call center or call sales offices being delivered to the target. The Spam source may also use a VoIP Spam initiator or a network of Spam initiators to initiate those calls on their behalf. These VoIP initiators could include compromised systems running Trojan software that are under the control of a spammer. All of these factors make it difficult to distinguish between legitimate VoIP and VoIP Spam.
There are essential distinctions that make the methods of detection and prevention of e-mail and IM spam not applicable to VoIP spam. As stated previously it is practically impossible to analyze the content of a future voice session. Further, the automated “accept-reject” decision must be made in real time in most of cases. “Accept” decision here means immediate delivery of the call directly to the recipient's terminal device including message servers, email servers or Instant messenger service.
Identification of the originator may be misleading in VoIP networks as the actual spam sender's identity may be anonymized and as a result, the recipient might see the identity of a legitimate signaling gateway as a call originator which it really could be in other legitimate scenarios.
Telephone number cannot be changed as often as temporarily assigned web-based e-mail addresses, so the assumption that a telephone number is public or known to the spammer must be made, i.e. in general for detection it is not possible to rely on setup failure reports resulting from the fact that recipients do not exist.